1. Field of the Invention
The present invention relates to a movable body, a travel device, and a movable body control method, and more particularly, to a movable body, a travel device, and a movable body control method for performing drive control based on own attitude information detected.
2. Description of Related Art
In recent years, there has been developed a movable body that detects own attitude information by using a gyro sensor, an acceleration sensor, or the like and performs drive control based on the detected attitude information. The movable body operates in accordance with an attitude control principle based on an inverted pendulum or in accordance with a ZMP (zero moment point) control principle for control on a two-legged robot, and detects its own attitude information from signals of an acceleration sensor and a gyro sensor mounted thereon. Then, the movable body operates a rotation command for a motor to maintain its own attitudes and transmits the rotation command data to a motor control device. Thus, the movable body can travel depending on a change in the center of gravity of a passenger while maintaining its own attitude based on the feedback control mentioned above.
For example, there has been proposed a travel device that travels while transporting a person and has various vehicle body compositions or vehicle structures for performing drive control based on own attitude information detected. For example, Japanese Unexamined Patent Publications Nos. 2006-211899 and 2006-315666 each disclose a coaxial two-wheel vehicle in which two wheels are coaxially provided. The coaxial two-wheel vehicle is in a structurally unstable state in a backward and forward direction and has a feature of stabilizing its attitude while controlling the wheels based on a feedback from an attitude sensor. In addition, the coaxial two-wheel vehicle is operated to move forwards or backwards or turn right or left in accordance with a command by shifting the center of gravity of a passenger, a command by tilting a step, a command from a control rod, or the like. Further, remote control by inputting a command from outside or autonomous locomotion on the basis of own trajectory planning is carried out in some cases.
It has now been discovered that a control system of a coaxial two-wheel vehicle that relates to the above invention requires a processing time period for computation to detect the attitude. Therefore, in order to realize a high-speed control cycle while maintaining a control performance, an attitude sensor that gives a rapid response and a controller (CPU (Central Processing Unit)) having a high computing power are required. Accordingly, an expensive system (CPU and attitude sensor) has to be used, leading to an increase in cost. In contrast, if a low-cost system is used, a control cycle slows, resulting in reduction in performance because of a loss of a control gain. For these reasons, there is a strong demand for a method of realizing a high-speed control cycle while maintaining a control performance with a low-cost system.
Hereinafter, a detailed description will be given on problems of a related coaxial two-wheel vehicle. In the related coaxial two-wheel vehicle, in a case where control on only at least one of a pitch angle and a pitch angular velocity of a vehicle is performed, or control on at least one of the pitch angle and the pitch angular velocity of the vehicle and control on at least one of a position, a velocity, a direction angle (yaw direction), and a direction velocity (yaw velocity) of the vehicle are performed at the same time, a torque command is generated based on a control system shown in FIG. 11 and is output to a motor amplifier in general. In an attitude controller 64 shown in FIG. 11, a vehicle pitch angle command, a vehicle pitch angular velocity command, and a vehicle position command, a vehicle velocity command, and the like are input, and control is performed based on deviations with a vehicle pitch angle, a vehicle pitch angular velocity, a vehicle position, a vehicle velocity, and the like that are detected by a detector 63. Examples of control by the attitude controller 64 include PID control, H infinity control, fuzzy control, and the like. In a turning controller 66, a yaw angle command, a yaw angular velocity command, and the like are input, and control is performed based on deviations with a vehicle yaw angle, a vehicle yaw angular velocity, and the like that are detected based on encoder information of a motor (not shown). Examples of control by the turning controller 66 include PD control, PID control, and the like.
FIG. 12 is a control block diagram showing a control system shown in FIG. 33 of Japanese Unexamined Patent Publication No. 2006-211899. The control system shown in FIG. 12 corresponds to a diagram that more specifically shows the control block diagram shown in FIG. 11. The attitude controller 64 shown in FIG. 11 is expressed by Expression (1) in paragraph 0013 of Japanese Unexamined Patent Publication No. 2006-211899 and a state feedback by gains K1 to K4 shown in FIG. 12. Further, the turning controller 65 shown in FIG. 11 is expressed by using gains K5 to K7 shown in FIG. 12, for example.
In the control system of the related coaxial two-wheel vehicle shown in FIG. 11, a torque command is obtained by performing an operation of addition or subtraction on a first torque command generated in the attitude controller 64 and a second torque command generated in the turning controller 66, and the torque command is output to a torque controller constituted of a motor amplifier, thereby performing drive control on wheels 62. Here, a control loop 71 for outputting the torque command includes a computation for attitude detection by the detector 63. Generally, a high-speed control cycle is required in the control loop 71 of the torque command, but the computation for the attitude detection takes time. Therefore, in order to complete the computation in the high-speed control cycle, a high-speed CPU (or attitude sensor capable of performing computation at high speed) is required, and thus the system becomes expensive. In contrast, in a case where the system is structured by a low-cost CPU (or low-cost attitude sensor) with the control cycle being slowed, harmful effects are caused in that the control performance relating to the pitch angle, the pitch angular velocity, the vehicle position, and the vehicle velocity is degraded (that is, the stability is lowered or command following capability is degraded) and a performance in the turning control is degraded (that is, a direction stability is lowered).
Further, when one of the wheels of the related coaxial two-wheel vehicle is away from the road surface during traveling, a load on the wheel that is away from the road surface decreases rapidly. Because robustness of the turning control is low, oscillations are generated between the wheel that is in contact with the ground and receives a larger load and the wheel that is away from the road surface and receives the smaller load, with the result that the vehicle may be vibrated in a turn direction and a dangerous state may be caused.
As described above, in the control system of the related coaxial two-wheel vehicle, the attitude detection processing that requires the computation time is included in the control loop of the torque command which requires the high-speed control cycle. For this reason, there is a problem in that the high-speed control cycle cannot be realized with the low-cost system while maintaining the control performance.
Accordingly, the present invention has an object to provide a movable body, a travel device, and a movable body control method that are capable of implementing higher-performance control by realizing the high-speed control cycle with a low-cost system while maintaining a control performance.